Four-rotor type rotary piston engine

ABSTRACT

A four-rotor type rotary piston engine including an eccentric shaft assembly composed of three elements; a main eccentric shaft defining the rotational axis of each rotor and first and second auxiliary eccentric shafts coupled to opposite end of the main eccentric shaft. The auxiliary eccentric shafts and the main eccentric shaft art fitted by tapered surfaces and have a small clearance therebetween in the radial direction to enable smooth coupling. The main eccentric shaft has two rotor eccentric journals for the second and the third cylinders. At first, the second and the third cylinders are installed. After that, the auxiliary eccentric shafts having rotor eccentric journals are coupled with the main eccentric shaft, and finally the first and the fourth cylinders are installed.

This application is a continuation of application Ser. No. 07/242,342,filed Sept. 9, 1988 abandoned.

FIELD OF THE INVENTION

The present invention relates to four-rotor type rotary piston engines,and more particularly to eccentric shaft structures for four-rotor typerotary piston engines and an installation method.

BACKGROUND OF THE INVENTION

As well known in rotary piston engines, an eccentric shaft with rotorjournal portions having axes offset to the axis of the eccentric shaftis disposed longitudinally extended in the center of the rotary pistonfor mounting eccentrically rotating rotors. Each rotor defines threecavities in the working chamber formed by the rotor housing having aninner wall of trochoidal configuration and a pair of side housingsattached to the end surface of the rotor housing abutting the workingchamber.

In the multiple-rotor type rotary piston engine having an eccentricshaft with rotor journal portions corresponding to each rotor, if thejournals of the eccentric shaft are provided between the rotor journalportions, the installation of the eccentric shaft into the enginehousing is difficult. Generally speaking, this difficulty relates to thegeometrical relation between larger rotor journal portions and smallereccentric journal portions. In case that the eccentric journal portionis as large as the rotor journal portion, though the installation may befacilitated, other serious problems, such as, escape of compressed gasthrough the eccentric journal portion are encountered. Therefore, theeccentric journal portions are formed smaller than the rotor journalportions.

In order to resolve the problem, an eccentric shaft assembly composed ofdivided eccentric shafts each of which corresponds to one of the rotorshas been proposed in the prior art, for example, in Japanese UtilityModel (Jikkosho) 45-8482. As proposed, the eccentric shaft assembly ismade for the four-rotor type piston engine. These divided eccentricshafts are connected in meshing engagement with each other, and areintegrated by one through bolt. Such an eccentric shaft assembly,however, has a weak point in tightness of connection because the boltmay be loosen by heat deformations or stress deformations. If the boltloosens, then unallowable vibration of the engine will be experienced.Also it is difficult to connect four divided eccentric shafts preciselyon the same common axis in view of production tolerances and errors.

On the other hand, Japanese Laid-open Patent Application No. (Tokkaisho)60-69208 shows another eccentric shaft structure having no through bolt.The eccentric shaft assembly of this publication is designed especiallyfor a three-rotor type piston engine, and therefore, is not capable foruse in a four-rotor type piston engine. Even if one were attempt to addanother rotor eccentric portion by way of an auxiliary eccentric shaftjoined with a main eccentric shaft so that the auxiliary eccentric shaftand the main eccentric shaft have two rotor eccentric portions,respectively, the eccentric shaft assembly would have unallowablevibration and one would have difficulty in centering of the shafts.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide aneccentric shaft structure for a four-rotor type rotary piston enginethat avoids the problems of the prior art and is easier and moreefficiently made and installed.

Another object of the present invention is to provide an eccentric shaftstructure capable of maintaining a proper rigidity.

A further object of the present invention is to provide an eccentricshaft structure having a suppressed and allowable vibration.

A still further object of the present invention is to provide aneccentric shaft structure which enables centering of shafts to beeffected easily.

Yet a further object of the present invention is to provide an eccentricshaft structure that enables its installation to be facilitated.

According to the present invention, the above and other objects can beaccomplished by providing a novel eccentric shaft structure for afour-rotor type rotary piston engine in accordance with the teachings ofthe present invention. The eccentric shaft assembly of the presentinvention is composed of three elements; a main eccentric shaft defininga rotational axis for each rotor, a first auxiliary eccentric shaft ofcylindrical configuration inserted on one end of the main eccentricshaft and a second auxiliary eccentric shaft of cylindricalconfiguration inserted on the other end of the main eccentric shaft. Themain eccentric shaft has an outer surface formed with an enlargeddiameter portion in its center portion, one smaller diameter portionintegrated through a tapered portion with one end of the larger diameterportion and another smaller diameter portion integrated through anothertapered portion with the other end of the larger diameter portion.

The first auxiliary eccentric shaft has an inner surface tapered to befitted to the tapered portion on one end of the larger diameter portion.The second auxiliary eccentric shaft has an inner surface tapered to befitted to the other tapered portion on the other end of the largerdiameter portion. The larger diameter portion of the main eccentricshaft has two rotor eccentric portions for a second rotor and a thirdrotor, respectively. The one smaller diameter portion with the firstauxiliary eccentric shaft fitted thereon provides a rotor eccentricportion for a first rotor. The other smaller diameter portion with thesecond auxiliary eccentric shaft fitted thereon provides a rotoreccentric portion for a fourth rotor.

Therefore, by fastening the first and the second auxiliary eccentricshafts onto both ends of the main eccentric shaft in the axialdirection, the first and the second auxiliary eccentric shafts areintegrally assembled with the main eccentric shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following descriptions of a preferredembodiment taking reference to the accompanying drawings.

FIG. 1 is an axially sectional view of a four-rotor type rotary pistonengine in accordance with one embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line II--II FIG. 1;

FIG. 3 is an axially sectional view showing a main eccentric shaft asinstalled in the engine of FIG. 1;

FIG. 4 is an axially sectional view showing a first auxiliary eccentricshaft as installed in the engine of FIG. 1;

FIG. 5 is an axially sectional view showing a second auxiliary eccentricshaft as installed in the engine of FIG. 1;

FIG. 6 is an axially sectional view showing side housings andintermediate housings defining the four rotor cylinder sections of FIG.1;

FIG. 7 is an enlarged axially sectional view showing a first embodimentof a coupling structure of the eccentric shaft assembly in accordancewith the present invention; and

FIG. 8 is an enlarged axially sectional view showing a second embodimentof a coupling structure of the eccentric shaft assembly in accordancewith the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 1. Structure of the Embodiment1.1. Housing Structure

Referring to FIG. 1, the engine has four cylinders; a first cylinder 2,a second cylinder 3, a third cylinder 4 and a fourth cylinder 5,numbered from left to right in FIG. 1. These cylinders 2, 3, 4 and 5 aredefined by four rotor housings 6, 7, 8 and 9 each having an inner wallsurface of trochoidal configuration, three intermediate housings 10, 11and 12 disposed between the rotor housings 6, 7, 8 and 9 and attached tothe side surfaces of the rotor housings 6, 7, 8 and 9, and side housings13 and 14 attached on the left end surface of the rotor housing 6 and onthe right end surface of the rotor housing 9, respectively. In thecylinder 2 (3, 4 and 5), there are defined three working chambers 15(16, 17 and 18) divided by the rotor 19 (20, 21 and 22 of substantiallytriangular configuration, as shown in FIG. 2.

These housings 6-14 are connected, spaced and positioned by hollow pins23, and are firmly connected by tightening bolts 24. In these housings6-14, cooling water passages 26 are provided so as to surround theworking chamber 15, 16, 17 and 18, and lubrication oil passage 27 isprovided to be insolated from the cooling water passage 26. The hollowpins 23 are communicated with the lubrication oil passage 27 so that thethrough holes of the hollow pins 23 act as a part of the lubrication oilpassage.

1.2. Rotor Supporting Structure

Rotors 19, 20, 21 and 22 are all of the same structure. Therefore, thefollowing description explaining the first cylinder 2, as arepresentative example, will apply with equal effect for all cylindersand rotors. In FIG. 2, a main eccentric shaft 32 is disposed along theaxis of cylinder 2 passing through substantially the center of the rotorhousing 6. A first auxiliary eccentric shaft 33 is fitted to or coupledon the outer surface of the main eccentric shaft 32. The main eccentricshaft 32 and the first auxiliary eccentric shaft 33 are connectedtogether by means of a key 36. A geared hub 411 is disposed around theperiphery of the first auxiliary eccentric shaft 33. This geared hub 411is, as illustrated hereafter in detail, fixed on the first side housing13 and is provided with a stationary external gear 414. The first rotor19 of substantially triangular configuration has an internal gear 415,which has a larger diameter than the external gear 414 and is fixedinside the center portion of the first rotor 19 by means of a pluralityof spring pins 194. By virtue of the meshing engagement of thestationary external gear 414 and the internal gear 415, the first rotor19 can rotate precisely along the trochoidal inner surface of the firstrotor housing 6. The first rotor 19 has, also, apex seals 191 and sideseals 192 for preventing the leakage of compressed gas between workingchambers.

The main eccentric shaft 32 has a lubrication oil passage 28 of athrough hole configuration. A part of the lubrication oil in the passage28 is introduced inside the first rotor 19 through an oil jet 195 so asto cool the first rotor 19 (See FIG. 1). Number 193 denotes an oil ring,and number 196 denotes a balancing hole for reducing the weight of thefirst auxiliary eccentric shaft. Number 29 denotes an ignition plug, andnumber 30 denotes an intake air port.

1.3 ECCENTRIC SHAFT ASSEMBLY STRUCTURE

In the engine 1, an eccentric shaft assembly 31 defining a rotationalaxis of each rotor is provided extended through the all cylinders. Asshown in FIGS. 3, 4 and 5, this eccentric shaft assembly 31 consists ofthree elements, the main eccentric shaft 32 and first and the secondauxiliary eccentric shafts 33, 34 coupled on opposite ends of the maineccentric shaft 32.

1.3.1 MAIN ECCENTRIC SHAFT

The main eccentric shaft 32 has an enlarged diameter portion 321 in thecenter region extending, at least, to cover the second and the thirdcylinders, and has first and second smaller diameter portions 322, 323,formed by reducing the ends in the regions where the first and thefourth cylinders, respectively, are mounted.

First tapered portion 324 is provided between the first smaller diameterportion 322 and the larger diameter portion 321, and second taperedportion 325 is provided between the second smaller diameter portion 323and the larger diameter portion 321. The larger diameter portion 321 hasan outer surface formed as second rotor eccentric journal portion 326for rotatably supporting the second rotor 20 and third rotor eccentricaljournal portion 327 for rotatably supporting the third rotor 21.

1.3.2 AUXILIARY ECCENTRIC SHAFTS

The first auxiliary eccentric shaft 33 is of cylindrical configuration,as shown in FIG. 4, and is coupled or fitted on the first smallerdiameter portion 322. The second auxiliary eccentric shaft 34 is ofcylindrical configuration, as shown in FIG. 5, and is coupled or fittedon the second smaller diameter portion 323. The first auxiliaryeccentric shaft 33 has an outer surface formed as first rotor eccentricjournal portion 331 for rotatably supporting the first rotor 19, and atapered inner surface formed as third tapered portion 332 adapted to befitted to the first tapered portion 324 on the main eccentric shaft 32,and also a cylindrical inner surface continuing from the tapered innersurface adapted to e fitted to the outer surface of the first smallerdiameter portion 322.

Therefore, the first auxiliary eccentric shaft 33 is fitted to the maineccentric shaft 32 by inserting the first smaller diameter portion 322of the main eccentric shaft 32 into the bore of the first auxiliaryeccentric shaft 33 and pressing them together in the axial direction,whereby the first auxiliary eccentric shaft 33 is correctly positionedon the same axis as the main eccentric shaft 32, while the first rotoreccentric journal portion 331 is located to be accommodated in the firstcylinder 2.

The second auxiliary eccentric shaft 3 is of substantially the samestructure as the first auxiliary eccentric shaft 33, having an outersurface formed as the fourth rotor eccentric journal portion 341 forrotatably supporting the fourth rotor 22, and a tapered inner surfaceformed as the fourth tapered portion 342 adapted to be fitted to thesecond tapered portion 325 on the main eccentric shaft 32, and also acylindrical inner surface continuing from the tapered inner surface andadapted to be fitted to the outer surface of the second smaller diameterportion 323.

1.3.3 THE COUPLING STRUCTURE OF THE ECCENTRIC SHAFT ASSEMBLY

More specifically, second auxiliary eccentric shaft 34 is constituted asshown in FIG. 7. Cylindrical inner surface 343 is adapted to be fittedto the outer surface of the second smaller diameter portion 323 andprovides a loose-coupling (in the radial direction) structure, someplay. In this embodiment and in a specific example thereof, the secondsmaller diameter portion 323 is designed to be 30.5 mm in its outerdiameter, and is produced within a tolerance of 0 to -12 μm. On theother hand, the second auxiliary eccentric shaft 34 is designed to be30.5 mm in its inner diameter at the surface 343, and is produced withina tolerance of +25 to 0 μm. Therefore, a clearance of average 20 μm(Min.0 μm ˜Max 37 μm) is provided between the second smaller diameter portion323 and the second auxiliary eccentric shaft 34. The second eccentricshaft 34 has a tapered axle portion 344 on the outer surface at its end.

Number 56 denotes a balancing weight having an inner surface formed as atapered hole 561 adapted to be fitted to the tapered axle portion 344.Number 70 denotes a nut, which is screwed onto the threaded end of thesecond auxiliary eccentric shaft 34, for pressing the balancing weight56 in the axial direction. The second auxiliary eccentric shaft 34 isfixed to the main eccentric shaft 32 by pressing the balancing weight 56in the axial direction by means of the nut 70.

Number 71 denote nut, which is screwed onto the threaded end 328 of themain eccentric shaft 32. Number 72 denotes a seal. The fourth bearingunit 47 has a through-hole 477 communicating to the lubrication oilpassage 27 at one end and to the hole 478 of the bearing 476 at theother end so that the lubrication oil can be introduced to the inside ofthe bearing 476.

1.3.4 SECOND EMBODIMENT OF THE COUPLING STRUCTURE OF THE ECCENTRIC SHAFTASSEMBLY

FIG. 8 shows another example of the coupling structure, wherein the maineccentric shaft 32' and the first auxiliary eccentric shaft 33' can besufficiently and tightly coupled by means of front pulley 64'. The firstauxiliary eccentric shaft 33' has an inner tapered surface 332' adaptedto be fitted to the tapered portion 324' of the main eccentric shaft 32'and has cylindrical inner surface 333' continuing from the inner taperedsurface 332' and adapted to be fitted to the outer surface of the firstsmaller diameter portion 322' in a loose-coupling structure like thatpreviously described. In a specific example, the loose-couplingstructure has substantially the same specification and productiontolerance as the above-mentioned first embodiment. The first auxiliaryeccentric shaft 33' has a tapered axle portion 334' on the outer surfaceat its end.

The front pulley 64' has an inner surface formed as a tapered hole 64'aadapted to be fitted to the tapered axle portion 334'. Number 73'denotes a nut, which is screwed onto the threaded end 335' of the firstauxiliary eccentric shaft 33', for pressing the front pulley 64' in theaxial direction.

Number 74' denotes a nut, which is screwed onto the threaded end 329' ofthe main eccentric shaft 33'.

1.4 BEARING STRUCTURE

Referring now to FIG. 6, the eccentric shaft assembly 31 is supported byfour bearing units 41, 43, 46 and 47, which are mounted on the sidehousing 13, 14 and the intermediate housings 10, 12, respectively.

1.4.1 THE FIRST BEARING UNIT

The side housing 13, consisting of a part of the first cylinder 2, holdsthe first bearing unit 41. Unit 41 includes geared hub 411 inserted inthrough-hole 42 on the side housing 13 and having a flange 412 extendingto the outside of the side housing 13. The central part of hub 411 is aninsertion 413. The flange 412 is fixed on the side surface of the sidehousing 13 by means of bolts 131. Inside of insertion 413 is a bearing416 for rotatably supporting the first auxiliary eccentric shaft 33. Onthe end of insertion 413 opposite flange 412 is mounted stationaryexternal gear 414 so that the stationary external gear 414 can be meshedwith the internal year 415 fixed on the side surface of the rotor 19facing the side housing 13.

1.4.2 SECOND BEARING UNIT

The second bearing unit 43 is a geared hub 431 comprised of an insertion432 inserted in through-hole 44 on intermediate housing 10, and fixed tothe intermediate housing 10 at its base end by means of bolts 101. Theinsertion 432 has mounted inside of it a bearing 433 for rotatablysupporting the larger diameter portion 321. The insertion 432 oppositeits bolted end has stationary external year 435 mounted on its end sothat the stationary external gear 435 can be meshed with internal gear434 fixed on the side surface of the rotor 20 facing the intermediatehousing 10.

1.4.3 THIRD BEARING UNIT

The third bearing unit 45 is of similar structure to the second bearingunit 43. Geared hub 451 has an insertion 452 inserted in through-hole 46on the intermediate housing 11, and is fixed to the intermediate housing11 at its base end by means of bolts 121. The insertion 452 has mountedinside of it a bearing 453 for rotatably supporting the larger diameterportion 321. The insertion 452 has a stationary external gear 455mounted on its free end so that the stationary external gear 455 can bemeshed with internal gear 454 fixed on the side surface of the rotor 21facing to the intermediate housing 12.

1.4.4 FOURTH BEARING UNIT

The fourth bearing unit 47 is of similar structure to the first bearingunit 41. Geared hub 741 has a flange 742 extending outside the sidehousing 14 and includes an insertion 473 inserted in through-hole 48 onthe side housing 14. The flange 472 is fixed on the side surface of theside housing 14 by means of bolts 141. The insertion 473 has mountedinside of it a bearing 476 for rotatably supporting the second auxiliaryeccentric shaft 34. The insertion 473 has a stationary external gear 475mounted on its free end so that the stationary external gear 475 can bemeshed with internal gear 474 fixed on the side surface of the rotor 22facing the side housing 14.

1.5 OTHER STRUCTURE

At one end of the eccentric shaft assembly 31 protruding from the sidehousing 13 to the left as shown in the FIG. 1, are provided balancingweight 41, driving gear 53 for driving first to third oil pumps 61, 62,and 63, and driving gear 80 of a distributor (not shown) all of whichare connected with the eccentric shaft assembly 31 by key 49 and arefastened in the axial direction by means of nut 54 threaded onto thethreaded end of shaft 32 The first auxiliary eccentric shaft 33 ispressed by the balancing weight 51 through thrust bearing 55 to couplefirmly the first auxiliary eccentric shaft 33 to the main eccentricshaft 32.

On the other hand, the other end of the eccentric shaft assembly 31protruding from the side housing 14 is similarly provided with balancingweight 56 and flywheel 57.

2. INSTALLATION PROCEDURE

The engine of the present invention is installed accordance with thefollowing procedure.

<Step 1>

The intermediate housing 11 is inserted between the second rotoreccentric journal portion 325 and the third rotor eccentric journalportion 327.

<Step 2>

The second rotor 20 is engaged with the second rotor eccentric journalportion 326, and the third rotor 31 is engaged with the third rotoreccentric journal portion 327. The second and the third rotor housings 7and 8 are positioned on opposite sides as of the intermediate housing 11by means of the hollow pins 23.

<Step 3>

The intermediate housing 10 carrying the second bearing unit 43 isplaced in position next to the second rotor eccentric journal portion326 so that the stationary external gear 435 can be meshed with theinternal year 434 fixed on the side surface of the rotor 20.

The intermediate housing 12 carrying the third bearing unit 45 is placedin position next to the third rotor eccentric journal portion 327 sothat the stationary external gear 455 can be meshed with the internalgear 454 fixed on the side surface of the rotor 31.

<Step 4>

The first auxiliary eccentric shaft 33 is coupled with the first smallerdiameter portion 322 through the key 36, and the second auxiliaryeccentric shaft 34 is coupled with the second smaller diameter portion323 through the key 37.

<Step 5>

The first rotor 19 is engaged with the first rotor eccentric journalportion 331 on the first auxiliary eccentric shaft 33, and the fourthrotor 22 is engaged with the fourth rotor eccentric journal portion 341on the second auxiliary eccentric shaft 34. The first rotor housing 6 ispositioned to the side of the intermediate housing 10 by means of thehollow pins 23, and the fourth rotor housing 9 is positioned to the sideof the intermediate housing 12 by means of the hollow pins 23.

<Step 6>

The side housing 13 carrying the first bearing unit 41 is place inposition next to the first rotor eccentric journal portion 331 so thatthe stationary external gear 414 can be meshed with the internal gear415 fixed on the side surface of the rotor 19. The side housing 14carrying the fourth bearing unit 47 is placed in portion next to thefourth rotor eccentric journal 341 so that the stationary external gear475 can be meshed with the internal gear 474 fixed on the side surfaceof rotor 22.

<Step 7>

All the housings are firmly fixed by means of tightening bolts 24.

<Step 8>

The first auxiliary eccentric shaft 33 and the second auxiliaryeccentric shaft 34 are firmly fixed by means of fasteners, such as,bolts.

3. MERITS OF THE PRESENT INVENTION COMPARED WITH THE PRIOR ART 3.1ECCENTRIC SHAFT STRUCTURE

The eccentric shaft assembly 31 of the present invention has a higherrigidity compared with the eccentric shaft assembly divided in the axialdirection a taught by the prior art, because the main eccentric shafthas enough length to pass through the entire engine and, thereforeaffords inherently sufficient rigidity. The eccentric shaft assembly 31is easily installed by inserting the main eccentric shaft to the bore ofthe auxiliary eccentric shaft. This enables easy centering of shafts tobe easy and the installation to be facilitated.

3.2 BEARING STRUCTURE

The location of the bearing units 41, 43, 45 and 47 in the presentinvention relative to the first and the second smaller diameter portions322, 323 of the main eccentric shaft 32 enables superior and effectivesuppression of deformation of the main eccentric shaft, because thesebearing units are located to support the small cross-sectional areas ofthe main eccentric shaft 32. Also, locating the two bearing units 41, 47on the side housings 13,14 brings the following merit. The side housings13, 14 have a larger flexibility and freedom to locate the bearing unitsthan the intermediate housings 10, 11 and 12. The bearing units 41, 47on the side housings 13, 14 can be designed to be big and thick enoughto stiffly support the eccentric shaft assembly 31, which leads tosuppression of deformation and vibration of the eccentric shaftassembly.

3.3 SUPPORTING STRUCTURE

The supporting structure of the present invention is characterized asfollows. The stationary external gear meshed with the internal gear ofthe rotor is supported by the respective outer housing of the cylinderwhen seen in the axial direction of the eccentric shaft assembly. Forexample, though the first rotor 19 can be supported by either of theside housing 13 and the intermediate housing 10, the stationary externalgear 414 is supported like a cantilever by the side housing 13 which islocated to the outer side in the axial direction. Location the fourbearing units according to above-mentioned layout is effective to lowervibration, especially at the far or remote end of the eccentric assemblywhich is more apt to swing.

3.4 LOOSE-COUPLING STRUCTURE

In accordance with the present invention, utilizing the loose-couplingstructure enables the main eccentric shaft and the auxiliary eccentricshaft to be smoothly fitted at the tapered surfaces.

Although the invention has been described with respect to specificpreferred embodiments, changes are possible without departing from thespirit and scope of the invention. Such changes as will be apparent tothose skilled in the art from the teachings of the present invention aredeemed to fall within the purview of the invention as claimed.

What is claimed is:
 1. A four-rotor rotary piston engine, comprising:anengine housing defining four rotor chambers therein; first to fourthrotors disposed in said four rotor chambers, respectively; and eccentricshaft means for mounting thereon said first to fourth rotors in saidrotor chambers and defining an axis of planetary rotation of said firstto fourth rotors, said eccentric shaft means including: a main eccentricshaft having a large diameter shaft portion formed at a middle portion,said large diameter shaft portion including second and third eccentricjournals for rotatably supporting thereon said second and third rotors,respectively, small diameter shaft portions located on opposite sides ofsaid large diameter shaft portion and a tapered shaft portion locatedbetween said large diameter shaft portion and each said small diametershaft portion; a first auxiliary eccentric shaft formed thereon with afirst eccentric journal for rotatably supporting thereon said firstrotor and an axially extending through hole formed at one end with atapered end so as to couple said first auxiliary eccentric shaft to saidmain eccentric shaft with said tapered end firmly contacting saidtapered shaft portion of said main eccentric shaft; a second auxiliaryeccentric shaft formed thereon with a fourth eccentric journal forrotatably supporting thereon said fourth rotor and an axially extendingthrough hole formed at one end with a tapered end so as to couple saidsecond auxiliary eccentric shaft to said main eccentric shaft with saidtapered end firmly contacting said tapered shaft portion of said maineccentric shaft; and at least one of said first and second auxiliaryeccentric shafts being formed with a cylindrical portion of the axiallyextending through hole having an internal diameter greater than anexternal diameter of a corresponding cylindrical portion of anassociated small diameter shaft portion to form a gap therebetween so asto be loosely mounted to an associated small diameter shaft portion ofsaid main eccentric shaft, thereby allowing said at least one of saidfirst and second auxiliary eccentric shafts to smoothly fit on said maineccentric shaft.
 2. A four-rotor rotary piston engine in accordance withclaim 1, further comprising fixing means for fixing said at least one ofsaid first and second auxiliary eccentric shafts on said main eccentricshaft so as to assemble said eccentric shaft means as an integral whole.3. A four-rotor rotary piston engine in accordance with claim 2, whereinsaid at least one of said first and second auxiliary eccentric shaftshas a tapered outer surface and said fixing means has a tapered borefitting on said tapered outer surface of said at least one of said firstand second auxiliary eccentric shafts.
 4. A four-rotor rotary pistonengine in accordance with claim 1, further comprising bearing meansdisposed in said housing for rotatably supporting said eccentric shaftmeans thereon.
 5. A four-rotor rotary piston engine, comprisingan enginehousing defining first to fourth rotor chambers therein; first to fourthrotors disposed in said four rotor chambers, respectively, each of saidrotors being provided with internal gear means fixed to a side surfacethereof; eccentric shaft means for mounting thereon said first to fourthrotors in said rotor chambers and defining an axis of planetary rotationof said first to fourth rotors, said eccentric shaft means including: amain eccentric shaft having a large diameter shaft portion formed at amiddle portion, said large diameter shaft portion including second andthird eccentric journals for rotatably supporting thereon said secondand third rotors, respectively, small diameter shaft portions located onopposite sides of said large diameter shaft portion and a tapered shaftportion located between said large diameter shaft portion and each saidsmall diameter shaft portion; a first auxiliary eccentric shaft formedthereon with a first eccentric journal for rotatably supporting thereonsaid first rotor and an axially extending through hole formed at one endwith a tapered end so as to couple said first auxiliary eccentric shaftto said main eccentric shaft with said tapered end firmly contactingsaid tapered shaft portion of said main eccentric shaft; a secondauxiliary eccentric shaft formed thereon with a fourth eccentric journalfor rotatably supporting thereon said fourth rotor and an axiallyextending through hole formed at one end with a tapered end so as tocouple said second auxiliary eccentric shaft to said main eccentricshaft with said tapered end firmly contacting said tapered shaft portionof said main eccentric shaft; at least one of said first and secondauxiliary eccentric shafts being formed with a cylindrical portion ofthe axially extending through hole having an internal diameter greaterthan an external diameter of a corresponding cylindrical portion of anassociated small diameter shaft portion to form a gap therebetween so asto be loosely mounted to an associated small diameter shaft portion ofsaid main eccentric shaft, thereby allowing said at least one of saidfirst and second auxiliary eccentric shafts to smoothly fit on said maineccentric shaft; and bearing means attached to a side wall of each ofsaid first to fourth chambers and having an external gear in mesh withsaid internal gear means for mounting thereon each of said first tofourth rotor.
 6. A four-rotor rotary piston engine in accordance withclaim 5, wherein said side surface of each of said first to fourthrotors to which said internal gear is fixed is on a side of each of saidfirst to fourth rotors remote from an axial center of said enginehousing with respect to each of said first to fourth rotors.
 7. Afour-rotor rotary piston engine in accordance with claim 5, wherein saidside wall of each of said first to fourth rotor chambers to which saidbearing means is attached is on a side of each of said first to fourthrotor chambers remote from an axial center of said engine housing withrespect to each of said first to fourth rotors.
 8. A method ofassembling a four-rotor rotary piston engine comprising an engine bodydefining first to fourth rotor chambers by an intermediate rotor housingand two end rotor housings fixed to opposite ends of said intermediaterotor housing, respectively, and eccentric shaft means for mountingthereon first to fourth rotors in said rotor chambers, respectively, anddefining an axis of planetary rotation of said first to fourth rotors,said eccentric shaft means including a main eccentric shaft having alarge diameter shaft portion formed at a middle portion, said largediameter shaft portion being formed thereon with second and thirdeccentric journals for rotatably supporting thereon said second andthird rotors, respectively, small diameter shaft portions located onopposite sides of said large diameter shaft portion and a tapered shaftportion located between said large diameter shaft portion and each saidsmall diameter shaft portion, first and second auxiliary eccentric shafteach formed thereon with an eccentric journal for rotatably supportingthereon each of said first and fourth rotors and an axially extendingthrough hole having at one end a tapered end so as to couple each ofsaid first and second auxiliary eccentric shafts to said main eccentricshaft with said tapered end firmly contracting said tapered shaftportion of said main eccentric shaft, said method comprising the stepsof:fitting said main eccentric shaft into said intermediate rotorhousing; rotatably mounting said second and third rotor on said secondand third eccentric journals of said main eccentric shaft; looselycoupling each said first and fourth auxiliary eccentric shafts onto anassociated smaller diameter shaft portion of said main eccentric shaftwith a gap between at least one of said first and fourth auxiliaryeccentric shafts and an associated smaller diameter shaft portion;attaching said two end rotor housings onto said main eccentric shaft;and tightening each said auxiliary eccentric shaft by fastening means soas to firmly fix each said auxiliary eccentric shaft to said maineccentric shaft.